Engine coolant change, engine now pinging when under load.

Discussion in 'Gen 2 Prius Technical Discussion' started by ZFORCE, Apr 23, 2019.


    ZFORCE Junior Member

    Mar 7, 2006
    Perth, Western Australia
    I have an 04 Australian model NHW20R with NO coolant storage tank (Thermos) or electric pump.

    I performed a coolant change on the engine, I took the radiator cap off, connected a hose to the little valve on the lower RHS of the radiator and let the coolant drain.

    I closed said valve and moved the hose to the bleeder on the top RHS of the radiator and opened the bleeder. I added coolant until it was coming out the bleeder hose.

    I closed the bleeder, started the engine and watched for any extra bubbles in the radiator fill neck. once satisfied I put the radiator cap back on and let the car warm up in inspection mode.

    Using the torque pro app on my phone I watched the engine come up to temperature (80 - 90c) and the radiator fan kicked in and out.

    I then took the car for a drive around the local area. One of the hills I normally drive up without issue, but today the car was pinging quite bad, honestly it sounded like someone shaking a can of spray paint under the bonnet. This was at maybe 1/2 throttle, accelerating harder to say 3/4 or full makes the noise go away.

    Bringing the car back to the workshop I let it cool and inspected the radiator level again, I found it had dropped just below the level of the filler neck, I topped it back up and performed a test drive again.

    What I found was the engine would not start pinging until the engine temperature go up to 80 - 90c. Prior to that loading up the engine with an accelerator/brake force charge would sound fine, after it reached temperature the engine would start pinging.

    The only thing I can think is there is still air trapped in the engine somewhere. The engine would rarely ping prior to the coolant change and when it did the computer corrected pretty quickly. I've tried to look for a bleed screw on the engine somewhere but I've not had any luck.

    The weather is not unusually warm or anything like that, we're coming into winter so temps are dropping. It's the same tank of fuel prior to the coolant work.

    My concern is that there is air trapped in the head causing a hotspot and pre-ignition. I'm open to any suggestions. The only other thing that was done at the same time was an oil change, 5w-30 and oil level is perfect.
    edthefox5 likes this.
  2. edthefox5

    edthefox5 Senior Member

    Jul 25, 2007
    Clearwater, Florida
    2007 Prius
    Wish you had posted about what you were going to do with the engine coolant I would have told you not to do it. The inverter coolant loop is much more important.

    The ice coolant loop is a pain in the tookus. Very very hard to get the air out unless you circulate the CHRS bottle pump because that’s where the air is stuck. you seem to know exactly what your doing though
    And rightly concerned about the head because as you know air lock goes to the highest part of the engine
    And unlike thousands of other posters who did the same as you and never monitored the engine temp
    It was refreshing to see You monitored your engine temp. Good job,

    Ok.....with the car off find the CHRS pump relay and find the contacts on the relay and then using a piece of wire
    Short across those contact positions in the fuse box to force run the CHRS pump, leave the rad cap off
    Run that pump with the car off for a bit and a good idea to connect a battery charger to the front jump points
    While doing this. While running the pump see if your getting bubbles in the rad and if the rad water level is going down. With the 12 volt battery charger connected you can run that pump with no issue.

    After doing this for a while and not
    T seeing anymore bubbles take the car for a ride and run the heat, while running heat listen closely
    Under the dash for any gurgling sounds or rushing water Sounds and see if you get good heat.
    Good heat no gurgling and engine staying at its 190 degrees you are ok.

    To any lurker it’s better idea to just dump the rad only and then fill it back up. This will not invoke air lock.
    Do it again in a few months. Really helps. And hassle free.

    Engine is easy on the ice coolant.
    Inverter is very hard on its coolant.

    Good luck.

    TMR-JWAP Senior Member

    Aug 12, 2016
    Columbia, SC
    2007 Prius
    I have an 04 Australian model NHW20R with NO coolant storage tank (Thermos) or electric pump.

    Those Aussies are smart. In hindsight, this was pretty much a useless add-on.
    Skibob likes this.